In the cyber era, the information transmission speed and communication mode which has been greatly improved subject to the development of sophisticated wireless communication devices, electronic device and network transmission technology. Nowadays, a variety of portable electronic apparatus are intensively used in our daily life as important means for wireless communication and network services. An electronic apparatus generally has a RTC (real time clock) installed in the circuit board thereof for recording system time. A real time clock is one of the requisite hardware devices of an electronic apparatus. The real time clock of an electronic apparatus uses a battery to provide the necessary working voltage for normal functioning when input power is off, eliminating the problem of resetting the time frequently.
FIG. 1 shows a real time clock charging circuit according to the prior art. According to this design, the real time clock charging circuit 1 is mounted on a circuit board, comprising a booting power input terminal 11, a standby power input terminal 12, a charging battery 13, a resistor 14, and a chip 15. The booting power input terminal 11 is adapted to receive a booting power. The standby power input terminal 12 is adapted to receive a standby power. The charging battery 13 is adapted to store electricity and to output it. The resistor 14 has one end electrically connected to the chip 15 and the other end electrically connected to the charging battery 13. The chip 15 is electrically connected to the real time clock. The chip 15 controls the flowing direction of the booting power, the standby power and the charging power.
Referring to FIG. 1 again, the chip 15 has a first input pin 151, a second input pin 152, a third input pin 153, and a power output pin 154. The first input pin 151 is electrically connected to the booting power input terminal 11. The second input pin 152 is electrically connected to the standby power input terminal 12. The third input pin 153 is electrically connected to one end of the resistor 14. The power output pin 154 is electrically connected to the real time clock to provide the real time clock with the necessary working power. During input of the booting power, the first input pin 151 receives the booting power. During input of the standby power, the second input pin 152 receives the standby power. The booting power and the standby power can be outputted to the real time clock through the power output pin 154, and transmitted through the third input pin 153 and the resistor 14 to the charging battery 13 for storage. When the booting power and the standby power are off, the charging battery 13 outputs the charging power through the third input pin 153 and the power output pin 154 to the real time clock. Thus, the necessary working power is constantly provided to the real time clock, keeping the real time clock to work continuously.
According to the aforesaid prior art real time clock charging circuit 1, the chip 15 is an important component that controls the flowing direction of power inputted from different power sources into the real time clock charging circuit 1. However, the complicated structure of the power input pins 151,152,153 and power output pin 154 of the chip 15 greatly increases the cost to install the chip 15 in the circuit board. Under the market trend to increase the density of component parts and chip sets in a circuit board, it is difficult to arrange the chip 15 in the limited space of the circuit board. The high cost of the chip 15 greatly complicates the design of the real time clock charging circuit and increases its manufacturing cost. Therefore, it is desirable to provide an inexpensive real time clock charging circuit that can easily be arranged on a circuit board.